Hi, I'm completely new to building a freetrack system. I wanted to use it for VR. Now, I saw these IR LEDs on Amazon (HERE), however I don't know how to proceed in building it. I would like a 3 point cap model, maybe powered from a microusb power bank (it says OUT 5V 1A).

Can you help me with a smiple schematic of the build? I'm so confused, I don't know if I need a resistor and, if I need one, which resistor do I need.

These are the specs of that ir-led as stated at Amazon
Forward Voltage: 1.3-1.6 V
Current: 20mA (maximum current?)

You need a resistor to limt the current to a maximum of 20mA(=0,02 A)
The voltage you have is 5V if you use that micro-usb powerbank.
You need to make a serial setup with these leds.You can calculate the resistor you need like this.
voltage powersource-(forward voltage leds x amount of leds)/ desired current= resistpr value you need
5V - (3x1,3V)/ 0,02A=55 ohm
5V - (3x1,6V)/ 0,02A=10 ohm
The resistor value must be between 10 ohm and 55 ohm.
But using these leds with maximum current with shorten their lifespan.

Because resistors are cheap I should just buy a few in different values in the range between 10 and 55 ohm.You start with the highest resistor and try which value gives the best result with your model.
You als probably need to file down the leds to get a better viewing angle.http://forum.free-track.net/index.php?showtopic=1908